The present invention relates to a liquid-cooled circuit device comprising a module of which circuit elements are mounted on a module base plate and in which the module is cooled by cooling liquid, and a method for manufacturing the liquid-cooled circuit device.
In an electronic circuit device having a power circuit element whose heat emission is high, such as an inverter device for controlling a driving motor of an electric vehicle, liquid cooling using a liquid having a greater thermal capacity is effective from the need to efficiently carry out cooling of the power circuit element. For prior art liquid cooling of a power circuit element, a direct heat transfer system by which a power circuit element is directly immersed in an electrically insulating cooling liquid and an indirect heat transfer system by which a circulating cooling liquid is brought into contact with a circuit case in which a power circuit element is mounted and the power circuit element is cooled by cooling the circuit case are mainly used.
However, the direct heat transfer system has a disadvantage of involving many incidental problems regarding leak, disposal and safety of special cooling liquid that is used. In the indirect heat transfer system, when the power circuit element is mounted in the circuit case, grease or the like has to be inserted between them to ensure heat transfer, and this leads to a disadvantage of poor cooling efficiency because the inserted substance obstructs heat radiation of the power circuit element.
As a way to obviate this disadvantage of the indirect heat transfer system, it is readily conceivable to mount the power circuit element on a base plate (hereinafter a device on which a power circuit element is mounted shall be referred to as a power module) and to bring the cooling liquid into contact with the other face (to be referred to as the back face) of the opposite to that on which the element is mounted, which would result in efficient cooling of the power circuit element. In this case, it is required to provide an opening in the circuit case and to close the opening by pressing the back face of the module base plate against the opening to bring the cooling liquid into direct contact with the back face of the module base plate. If there is any gap in the contacting part of the back face of the module base plate pressed against the circuit case opening, the cooling liquid will enter through the gap into the circuit case to cause the module and electronic circuits in the circuit case to be immersed in the cooling liquid and thereby invite erroneous actions by the electronic device.
Then, in order to resolve this problem, a solution is proposed in JP-A-11-163572 specification, according to which the module base plate and the cooling liquid case are joined with screws or the like, and an O-ring is provided inside to seal any gap between them, so that even if the cooling liquid in the cooling liquid case leaks, the leaked liquid will not directly enter the circuit case but will be discharged into the atmosphere.
However, the technique described in JP-A-11-163572 specification requires a portion on the module base plate for mounting the O ring, screws and so forth, and therefore involves the problem that size of the module base plate becomes large. Such an enlarged module base plate not only adds to the cost, because the module base plate itself is rather expensive essentially, but also, where a large number of power modules are to be mounted, the spacing between the power circuit elements would be expanded, resulting in an increased size of the whole device.
In view of these problems of the prior art, an object of the present invention is to provide a liquid-cooled circuit device contributing to preventing the module base plate from expanding in size and the cooling liquid from infiltrating into the circuit case, and a manufacturing method for such a circuit element device.
A liquid-cooled circuit device according to a first aspect of the present invention, comprising: a module comprising a module base plate and a circuit element mounted on the module base plate; a circuit case for housing the module; a cooling case through which cooling liquid flows, said cooling liquid being in contact with a back face of the module base plate; and a module supporting having an opening for accommodating the module base plate therein; wherein said module base plate is placed into said opening of said module supporting plate, edges of the opening and the module base plate are joined by welding to each other without a gap therebetween; said circuit case is formed with an opening smaller than said module supporting plate; said module supporting plate is fixed to the circuit case so as to block said opening in said circuit case from outside the circuit case and to cause said circuit element of said module mounted on the module supporting plate to be positioned within the circuit case; said cooling case is formed with a recess forming a cooling liquid chamber through which the cooling liquid flows; and said cooling case is fixed to said circuit case so that said recess faces said module supporting plate.
With the structure described above, the module base plate and the module supporting plate can be regarded as an integrated structure by welding, there is no conceivable risk of liquid leakage from between them. Furthermore, since the module supporting plate is greater in size than the opening in the circuit case and blocks the opening from outside the circuit case, even if the cooling liquid leaks from between the supporting plate and the circuit case, the leaked liquid will be discharged outside instead of entering the circuit case and soaking circuit elements, base plates and wiring arranged in the circuit case because a connecting portion between them are positioned outside the circuit case. Further, as the back face of the module base plate faces the inside of the cooling case from the opening in the module supporting plate, the back face of the module base plate is in direct contact with the cooling liquid in the cooling case to efficiently cool the module. Moreover, since the module base plate is joined to the module supporting plate by welding, there is no need for the module base plate to be provided with any O ring for sealing or screws for connection, making it easier to reduce the size of the module base plate. Furthermore, since the module is mounted inside the circuit case, terminal wiring to the control circuit is simplified. To add, while welding usually means a method of melting the parts to be joined, and has such versions as arc welding, laser welding, electron beam welding and the like, there are methods by which the parts to be joined are not melted, such as soldering, brazing, friction stir welding and the like. In present specification, xe2x80x9cweldingxe2x80x9d is as a generic term for both categories of joining methods. It has to be noted, however, that welding of a module base plate on which a circuit element is mounted should preferably be accomplished by a friction stir welding method to minimize the thermal impact on the circuit element and other members.
A liquid-cooled circuit device according to a second aspect of the invention, comprising: a module comprising a module base plate and a circuit element mounted on the module base plate; a circuit case for housing the module; and a cooling case through which cooling liquid flows, said cooling liquid being in contact with a back face of the module base plate; wherein said circuit case is formed with an opening; said cooling case is formed with a recess forming a cooling liquid chamber through which said cooling liquid passes; the module base plate is arranged so that the circuit element of the module be positioned inside the circuit case, and joined by welding to either an edge of the opening in said circuit case or an edge of an opening of said recess of said cooling case without a gap therebetween; and said cooling case is fixed to the circuit case so that said recess faces toward said opening in said circuit case.
With the structure described above, the module base plate and the edge of the opening in the circuit case or the module base plate and the edge of the opening in the cooling case form a structure integrated by welding, and accordingly there is no conceivable risk of liquid leakage from between them. In other words, the inside of the circuit case to which the module base plate is fitted is in a completely sealed state. Therefore, there is no risk of cooling liquid leaked from inside the cooling case to enter the circuit case. Also, similar to the liquid-cooled circuit device according to the first aspect of the invention, the present device can also cool the module efficiently, and makes it easier to reduce the size of the module base plate. Furthermore, this structure allows the number of parts to be reduced than the first embodiment of the liquid-cooled circuit device.
A liquid-cooled circuit device according to a third aspect of the invention, comprising: a module comprising a module base plate and a circuit element mounted on the module base plate; and a circuit case for housing the module; wherein: the module base plate is placed within said circuit case so as to partition inside of the circuit case into two chambers, and is joined to an inner face of the circuit case by welding without a gap therebetween; one of the two chambers formed in said circuit case, on the side where the circuit element of the module is present, forms a circuit accommodating chamber and the other forms a cooling liquid chamber; and said cooling liquid chamber is formed with an inlet and outlet for cooling liquid flowing in contact with a back face of the module base plate of the module.
Also with this structure, in dividing the inside of the circuit case by the module base plate, it is joined by welding to the inner face of the circuit case without a gap therebetween, so that the cooling liquid from one of the two chambers, i.e. the cooling liquid chamber, does not enter the other chamber, the circuit accommodating chamber. Moreover, this structure dispenses with sealing members such as O rings and connecting members such as screws, resulting in an even smaller number of parts.
Moreover, in the third embodiment of the liquid-cooled circuit device, if some of the parts forming the cooling liquid chamber among the case forming parts constituting the circuit case are detachably fixed to the rest of the case forming parts, maintenance and other tasks can be accomplished with greater ease though the number of parts somewhat increases.
A method for manufacturing a circuit element device to achieve the object is characterized in that a base plate on which a circuit element is mounted and other member are joined by a friction stir welding method utilizing a plastic flow due to friction heat generated by rotation of a rotary tool. It is preferable here for the base plate and the other member to contain the same metallic element.
A circuit element device for achieving the object is characterized in that a base plate on which a circuit element is mounted and other member are joined to each other by welding, and crystal grains in parts joined by welding are smaller than the original crystal grains of the respective members. A liquid-cooled circuit device comprising: a module having a circuit element and a module base plate on surface of which the circuit element is mounted; a circuit case for accommodating said module; and a cooling liquid chamber for flowing a cooling liquid in contact with a back face of said module base plate of said module, wherein said module base plate of said module is fitted into an opening provided in a member forming said cooling liquid chamber and welded without a gap.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.